After oil is taken out from rig it must be transported to oil refineries. Tankers are the most cost effective transportation method. Tankers are normally build very largely. The largest ship "Knock Nevis". She is 458 metres (1504 feet) in length and 69 m (226 ft) in width and can carry nearly 4.1 million of petroleum.
The following video clip show you its reconstruction after accident. You can imagine the size of it by comparing with other objects .
This is a picture on "Knock Nevis"
This is the biggest of crude oil tankers in this world.